The preferred embodiment relates generally to a strategy for controlling a motor vehicle transfer case clutch. More particularly, it pertains determining and applying a desired duty cycle to a coil that actuates the clutch in response to a current torque magnitude in the driveline.
An automotive vehicle driveline whose powertrain has electronic engine throttle control is able to maintain a moderately high magnitude of torque during a period after the driver has released the accelerator pedal. A driveline system that preemptively engages its 4WD system based on driver intent is susceptible to wheel slip on surfaces having a low coefficient of friction. A vehicle driveline that simply engages its transfer clutch and produces 4WD engagement with reference to engine torque is at risk of inadvertent engagement during engine idle conditions when engine idle torque is high.
A motor vehicle driveline with 4WD clutches that tend to exhibit some degree of stick-slip may experience a bump or bang as the clutch is turned off and energy trapped by the clutch is suddenly released.
There is need for a driveline system that eliminates wheel slip due to off-throttle residual torque, that does not bind-up in turns, that only activates on slippery road surfaces, thereby reducing the possibility of customer-detectable NVH associated with clutch engagement, and that prevents occurrence of a bump when the transfer clutch releases.